Magnetic amplifier circuit breaker



July 14, 1959 M. P. SIEDBAND MAGNETIC AMPLIFIER cmcurr BREAKER Filed Oct. 5, 1955 INVENT OR MELVIN P. .SIEDBAND ATTORNEYS United Sttes 2,895,084 MAGNETIC AMPLIFIER CIRCUIT BREAKER Application October 5, 1955, Serial No. 538,817 Claims. (Cl. 317-22) This. invention relates. to circuit breakers with special application to protection of electrical apparatus from overloads.

For many uses, such as for protection of radar modulator high voltage apparatus, a circuit breaker should be highly sensitive and at the same time resistant to shock, vibration, temperature change and other environmental conditions which tend to diminish the effectiveness of the device.

Accordingly, a primary object of the invention is to provide a circuit breaker which is highly sensitive in its action. Other objects include provision of a circuit breaker which is resistant to disturbances produced by shock, which functions satisfactorily under conditions of vibration, and which is largely independent of temperature variations.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing wherein the various apparatus and circuits of the circuit breaker are diagrammatically indicated.

Referring to the figure, there is indicated two circuit sections A and B, A being applied to the circuit breaker section and B to the load unit which, in this disclosure, is a radar modulator high voltage supply unit.

The circuit breaker A includes the full wave self-saturating type magnetic amplifier 10, the control circuit 11 including control coils 12 and 13, the bias circuit 14 including bias coils 15 and 16, the rectifier bridge 17, the time delay relay 18, the main relay 19, the overload tester 20, and the reset circuit 21, all appropriately connected for functioning. Ingreater detail, magnetic amplifier takes the form of two reactor coils 30 and 31 connected in parallel to a source of electric power through manual switch 29, which, for the indicated use, may be 115 volts alternating current at 400 cycles. Current derived from this source after passing through the coils 30 and 31 and rectifiers 33 and 34 is combined in conductor 35 and led through the full-wave bridge 17, which may be of the selenium rectifier type, to the cored relay coil 36 of relay 19. Passage of current as described, however, is contingent on the saturation of the reactor cores 37 and 3810f coils'30 and 31 by the rectified current.

As shown, the relay 19 is in its deenergized position with switch arm 40, which is grounded at 41, having connection through contact 42 to the primary coil 43 of the plate transformer 44 in the Bcircuit section. in its energized position switch arm 40 is open. Other elements of the B-circuit include the plate transformer secondary 45, tubes 46 and 47 connected in series with the transformer secondary and the resistor 43 connected to the series circuit between tubes 46 and 47 and grounded at 49.

In the deenergized relay position, also, the relay 19 has a circuit connection through switch arm 50 from the bias circuit 14 to the overload tester 20 and reset circuit 21. The overload tester includes switch contact 51 and atent 3 Patented July 14,. 1959 resistor 52 connected in series to ground at 53, and an alternative circuit through contact 54 and resistors 55 and 56 to ground. A capacitor 57, which may be variable, is connected across these two branch circuits at the grounded ends of resistors 52 and 55. A conductor 60 leads from a point between resistors 55, 56 through manual switch 61 and resistor 62 to ground at 63, a variable capacitor 64 being connected in shunt around resistor 62. This capacitor-resistor-switch unit constitutes the reset circuit 21.

The bias circuit 14 is connected at one end to the pivot 67 of relay switch arm 50 and from this point passes through bias coils 15 and 16 and normally open time delay relay switch 68 to a source 69 of direct current through manual switch 24 at 250 volts. The time delay relay switch is actuated by a non-inductive resistor 70 which is grounded at one end and at the other connects to the power line 71. This line joins the plate transformer primary 43 in the B section to a source terminal 72 through manual switch 73 for power at 115 volts 400 cycles, a 15 second time delay unit 7 4, which may be structurally similar to time delay unit 18, being inserted in line 71. It is pointed out that the winding direction of bias coils 15 and 16 is such as to unsaturate amplifier coils 30 and 31, when coils 15 and 16 are energized;

The control circuit 11 leads from a ground connection at 75 through amplifier control coils 12 and 13 to the mid-point of secondary 45 of the plate transformer 44 in the B section. A tap is made in this circuit from the transformer side of control coil 13 at 76 to a slide 77 movable on grounded resistor 78 to secure a desired level of current flow in the control circuit. The Winding direction of control coils 12 and 13 is such as to augment the saturating flow in amplifier coils 30 and 31 when coils 12 and 13 are energized.

The operation ofthe device may now be described. Assume that power is applied. to the input terminals 32, 69 and 72 at the described values. Bias circuit 14, connecting to the 250 volt direct current source at 69-, remains open because of time delay switch 68 but is subject to closure in 45 seconds. The B-circuit, connecting to source terminal 72, remains open for 15 seconds due to time delay unit 74. However, the magnetic amplifier circuit is at once energized, the coils 30 and 31 becoming saturated by the rectified current through these coils and thus permitting current flow through the relay coil 36 of relay 19. The relay switch 40 is accordingly moved to open position.

In 15 seconds, power is applied from source terminal 72 to time delay unit 18, the B-circuit remaining deenergized due to open switch 40. In 45 seconds, power from source terminal 69 is applied to the bias circuit by closure of time delay switch 68, the direct current of this source passing directly to ground through overload tester resistors 55 and 56 and giving capacitor 57 a partial'charge. Thereupon, the saturating flux in the amplifier is reduced by bias coils 15 and 16 to such an extent that relay 19 is deenergized, switch arms 40: and; 5.0 returning to the position as shown in the figure with the Bcircuit completed through ground 41 and the bias circuit completed through the alternative tester branch including resistor 52 and conductor 58. The B-circuit power will now be maintained unless overload values develop in excess of the level set by slider 77 in the control circuit 11. Should this occur the control coils 12 and 13 add sufficient flux to the amplifier to again saturate it, thereby breaking the B-circuit at relay contact 42 and moving switch arm 50 to contact 54 when capacitor 57 receives another increment of charge.

Since the control coil circuit is opened by the relay action, the bias circuit 14 again becomes effective and again the amplifier is unsaturated and high voltage is applied to the B-circuit by relay movement. If the overload still exists the control circuit 11 again functions and the capacitor again receives an increment of charge. With continued overload this cycle is repeated until the capacitor is charged to the point where unsaturating bias current cannot flow and the B-circuit remains continuously open.

The number of recycling tests may, of course, be varied by the constants of the circuit, including capacitor 57, a four time test being found adequate for most uses. After the test period with the B-circuit remaining open, recycling can be continued by the reset unit 21, the capacitor 64, connected by manual switch 61, forming a shunt to ground around capacitor 57.

It will now appear that the load protecting device, as described, has no elements particularly susceptible to shock, vibration, temperature or other environmental conditions. The device, also, is highly sensitive as compared to conventional systems and is advantageous from the viewpoint of weight and spaced due to absence of differential relays, power contactors, resistance-capacitance nets, and the like. It is pointed out, further, that it is impossible to override the circuit breaker by holding the reset switch closed.

Additional control windings may be incorporated on the reactors such that when the sum of each of the currents in these windings exceeds a neutralization current in an additional winding, the reactor core will saturate, closing the relay. In this manner, the device may protect a number of circuits from overload.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. 'It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A circuit breaker device for circuits susceptible to overloads comprising a load circuit, a first source of alternating current, a manual switch in said load circuit, a normally closed load switch connected in series to said load circuit and current source, a relay for moving said switch to open position, a second source of alternating current, a direct current saturable reactor connected between said second alternating current source and said relay to supply actuating energy thereto, a source of direct current, bias means connected to said direct current source for applying said direct current to said reactor to unsaturate the same whereby the relay is deenergized, control means connected to said load and reactor for neutralizing intermittently said bias means when the load current exceeds a predetermined value, means for terminating the intermittent neutralization of said bias means after a limited number of neutralizations, during continuance of excess load in said load circuit, and time delay means for preventing flow of load current through said normally closed load switch for a time period after closure of said manual switch but before closure of said constant direct current bias circuit.

2. The circuit breaker device as defined in claim 1 with means for starting a second series of bias means neutralizations by said control means and additional means for terminating said second series of bias means 4 neutralizations, during continuance of excess load in said load circuit, said neutralization terminating means being independent of said first named neutralization terminating means.

3. A circuit breaker device for circuits susceptible to overloads comprising a load circuit, a first source of alternating current, a normally closed load switch connected in series to said load circuit and current source, a relay for moving said switch to open position, a second source of alternating current, a direct current saturable reactor connected between said second alternating current source and said relay to supply actuating energy thereto, a source of direct current, bias means connected to said direct current source for applying said direct current to said reactor to desaturate the same whereby the relay is deenergized, and control means connected to said load and reactor for neutralizing said bias means when the load current exceeds a predetermined value, whereby the load circuit is broken and the control means deenergized, said load circuit including a transformer having a primary coil and a load connected secondary coil, said load switch and first current source being connected in series with said transformer, and said control means being connected between ground and the mid-point of said secondary coil.

4. A circuit breaker device for circuits susceptible to overloads comprising a load circuit, a first source of alternating current, a normally closed load switch connected in series to said load circuit and current source, a relay for moving said switch to open position, a second source of alternating current, a direct current saturable reactor connected between said second alternating current source and said relay to supply actuating energy thereto, a source of direct current, bias means connected to said direct current source for applying said direct current to said reactor to unsaturate the same whereby the relay is deenergized, control means connected to said load and reactor for neutralizing intermittently said bias means when the load current exceeds a predetermined value, and means for terminating the intermittent neutralization of said bias means after a limited number of neutralizations, during continuance of excess load in said load circuit, said load circuit including a transformer having a primary coil and a load connected secondary coil, said load switch and first current source being connected in series with said transformer, and said control means being connected between ground and the midpoint of said secondary coil.

5. The circuit breaker as defined in claim 3 including additionally means for delaying flow of current from said first alternating current source until after current flow is begun in said second alternating current source and means for delaying current flow from said direct current source until after current flow is begun from said second alternating current source.

References Cited in the file of this patent UNITED STATES PATENTS 2,125,157 Gamel July 26, 1938 2,706,764 Mitchell Apr. 19, 1955 2,766,419 Miller Oct. 9, 1956 

